with, or repugnant to, its express terms.1 So, the immemorial existence of certain rights or exemptions, as a modus or a claim to the payment of tolls, may be inferred from uninterrupted modern usage.2

The

*Lastly, evidence of usage is likewise admissible to aid in [*719] interpreting acts of Parliament, the language of which is doubtful; for jus et norma loquendi are governed by usage. meaning of things spoken or written must be such as it has constantly been received to be by common acceptation,3 and that exposition shall be preferred, which, in the words of Sir E. Coke,' is "approved by constant and continual use and experience :" optima enim est legis interpres consuetudo.

We shall conclude these very brief remarks upon the maxim optimus interpres rerum usus in the words of Mr. Justice Story, who observes, "The true and appropriate office of a usage or custom is, to interpret the otherwise indeterminate intentions of parties, and to ascertain the nature and extent of their contracts, arising, not from express stipulations, but from mere implications and presumptions, and acts of a doubtful or equivocal character. It may also be admitted to ascertain the true meaning of a particular word, or of particular words in a given instrument, when the word or words have various senses, some common, some qualified, and some technical, according to the subject-matter to which they are applied. But I apprehend that it can never be proper to resort to any usage or custom to control or vary the positive stipulations in a written contract, and, à fortiori, not in order to contradict them. An express contract of the parties is always admissible to supersede, or vary or control a usage or custom; for the latter may always be waived at the will of the parties. But a written and express contract cannot be controlled, or varied, or contradicted by a usage or

1 Per Lord Kenyon, C. J., Withnell v. Gartham, 6 T. R. 398; Rex v. Salway, 9 B. & C. 424, 435; E. C. L. R. 17; Stammers v. Dixon, 7 East, 200; per Lord Brougham, C., Attorney-General v. Brazen Nose Coll., 2 Cl. & Fin. 317; per Tindal, C. J., 8 Scott, N. R. 813; ante, p. 532, n. 2.

2 See per Parke, B., Jenkins v. Harvey, 1 Cr., M. & R. 894;(*) per Richardson, J., Chod v. Tilsed, 2 B. & B. 409; E. C. L. R. 6; Earl of Egremont v. Saul, 6 Ad. & E. 924; E. C. L. R. 33; Rex v. Joliffe, 2 B. & C. 54; E. C. L. R. 9; Brune v. Thompson, 4 Q. B. 543; E. C. L. R. 45.

3 Vaughan, R. 169; Argument, Rex v. Bellringer, 4 T. R. 819.

4 2 Inst. 18.

5 D. 1, 3, 37; per Lord Brougham, 3 Cl. & Fin. 354; cited, ante, p. 533.

[*720] custom; *for that would not only be to admit parol evidence to control, vary, or contradict written contracts; but it would be to allow mere presumptions and implications, properly arising in the absence of any positive expressions of intention, to control, vary, or contradict the most formal and deliberate declarations of the parties."1

CUILIBET IN SUA ARTE PERITO EST Credendum.
(Co. Litt. 125, a.)

Credence should be given to one skilled in his peculiar profession.

Almost all the injuries, it has been observed, which one individual may receive from another, and which are the foundation of numberless actions, involve in them questions peculiar to the trades and conditions of the parties; and, in these cases, the jury must, according to the above maxim, attend to the witnesses, and decide according to their number, professional skill, and means of knowledge. Thus, in an action against a surgeon for ignorance, the question may turn on a nice point of surgery. In an action on a policy of life insurance, physicians must be examined. So, for injuries to a mill worked by running water, and occasioned by the erection of another mill higher up the stream, millwrights and engineers must be called as witnesses. In like manner, many questions respecting navigation arise, which must necessarily be decided by a jury, as in the ordinary case of deviation on a policy of marine insurance, of seaworthiness, or where one ship runs down another at sea in consequence of bad steering.'

[*721]

*Respecting matters, then, of science, trade,3 and others of the same description, persons of skill may not only speak as to facts, but are even allowed to give their opinions in evidence," which is contrary to the general rule, that the opinion of a witness is not evidence. Thus the opinion of medical men is evidence as to the state of a patient whom they have seen; and, even in cases where they have not themselves seen the patient, but have heard the symptoms and particulars of his state detailed by other witnesses at

1 The Schooner Reeside, 2 Sumner, R. (U. S.) 567.

2 Johnstone v. Sutton (in error), 1 T. R. 538, 539.

3 The importance attached to the lex mercatoria, or custom of merchants, may be referred to this maxim. See 1 Bla. Com. 75.

41 Stark. Ev., 3d ed. 173, 175.

5 2 Phil. Ev., 8th ed. 899.

the trial, their opinions on the nature of such symptoms have been admitted. In prosecutions for murder, they have, therefore, been allowed to state their opinion, whether the wounds described by witnesses were likely to be the cause of death.2

With respect to the admissibility in evidence of the opinion of a medical man as to the state of mind of a prisoner when on his trial for the alleged offence, the following question was recently proposed to the judges by the House of Lords: "Can a medical man, conversant with the disease of insanity, who never saw the prisoner previous to the trial, but who was present during the whole trial and the examination of all the witnesses, be asked his opinion as to the state of the prisoner's mind, at the time of the commission of the alleged crime, or his opinion whether the prisoner was conscious, at the time of doing the act, that he was acting contrary to law, or whether he was labouring under any, and what, delusion at the time?" To the question thus proposed, the majority of the judges returned the following answer, which removes much of the *dif[*722] ficulty which formerly existed with reference to this, the most important practical application of the maxim under review, and must be considered as laying down the rule upon this subject: "We think the medical man, under the circumstances supposed, cannot, in strictness, be asked his opinion in the terms above stated, because each of those questions involves the determination of the truth of the facts deposed to, which it is for the jury to decide, and the questions are not mere questions upon a matter of science, in which case such evidence is admissible. But where the facts are admitted. or not disputed, and the question becomes substantially one of science only, it may be convenient to allow the question to be put in that general form, though the same cannot be insisted on as a matter of right."

Further, on the principle expressed by the maxim cuilibet in suâ arte perito est credendum, ship-builders have been allowed to state their opinions as to the seaworthiness of a ship from examining a survey which had been taken by others, and at the taking of which they were not present; and the opinion of an artist is evidence as to the genuineness of a picture. But, although witnesses conversant with

3

Ib.; Wright's case, Russ. & Ry. Cr. C. 456.

2 See 8 Scott, N. R. 603.

32 Phil. Ev., 8th ed. 901. So, evidence as to the genuineness of handwriting given by a witness possessing the requisite experience and skill is admissible, although little or no weight has, by many judges, been thought to be due to testi

2

1

a particular trade may be allowed to speak to a prevailing practice in that trade, and although scientific persons may give their opinion on matters of science, it has been expressly decided, that witnesses are not receivable to state their views of matters of legal or moral obligation, nor on the manner in which others would probably have been influenced if particular parties had acted in one *way [*723] rather than another. For instance, in an action on a policy

of insurance, where a broker stated, on cross-examination, that in his opinion certain letters ought to have been disclosed, and that if they had, the policy would not have been underwritten; this was held to be mere opinion, and not evidence.2 And, in like manner, it seems, notwithstanding some conflicting decisions, that the opinions of underwriters as to the materiality of facts, and the effect they would have had upon the amount of premium, would not, in general, be admissible in evidence; it being the province of the jury, and not of any witness, to decide what facts ought to be communicated.3 Where, however, the fixing the fair price and value upon a contract to insure is a matter of skill and judgment, and must be effected according to certain general rules and principles of calculation applied to the particular circumstances of each individual case, it seems to be matter of evidence to show whether the fact suppressed would have been noticed as a term of the particular calculation. In some instances, moreover, the materiality of the fact withheld would be a question of pure science: in others, it is very possible, that mere common sense, although sufficient to comprehend that the disclosure was material, would not be so to understand to what extent the risk was increased by that fact; and, in intermediate cases, it seems difficult in principle wholly to exclude evidence of the nature alluded to, although its importance may vary exceedingly according to circumstances. Thus, it has been said,' that the time of sail

[*724]ing may be very material to the risk. How far it is so, must

mony of this description. 2 Phil. Ev., 9th ed. 254; 2 Stark. Ev., 3d ed. 512; Doe d. Mudd v. Suckermore, 5 Ad. & E. 703; E. C. L. R. 31; Doe d. Jenkins v. Davies, 16 L. J., Q. B. 218.

1 Judgment, Campbell v. Rickards, 5 B. & Ad. 846; E. C. L. R. 27; where the previous conflicting decisions are cited: Ramadge v. Ryan, 9 Bing. 333; E. C. L. R. 23. See, however, Chapman v. Walton, 10 Bing. 57; E. C. L. R. 25. Refer also to Greville v. Chapman, 5 Q. B. 731; E. C. L. R. 48.

2 Carter v. Boehm, 3 Burr. 1905, 1913, 1914.

3 Per Gibbs, C. J., Durrell v. Bederly, Holt, N. P. C. 285. See note 1, supra; Park on Mar. Insur. 8th ed. 806. 4 3 Stark. Ev., 3d ed. 887, 888.

5 Per Story, J., delivering Judgment, M'Lanahan v. The Universal Insurance Company, 1 Peters, R. (U. S.) 188.

essentially depend upon the nature and length of the voyage, the season of the year, the prevalence of the winds, the conformation of the coasts, the usages of trade as to navigation and touching and staying at port, the objects of the enterprise, and other circumstances, political and otherwise, which may retard or advance the general progress of the voyage. The material ingredients of all such inquiries are mixed up with nautical skill, information, and experience, and are to be ascertained in part upon the testimony of maritime persons, and are in no case judicially cognisable as matter of law. The ultimate fact itself, which is the test of materiality, that is, whether the risk be increased so as to enhance the premium, is, in many cases, an inquiry dependent upon the judgment of underwriters and others who are conversant with the subject of insurance.

In a recent and important case will be found a good illustration of the above maxim as it applies to the legal knowledge of a party, whose evidence it is proposed to take. In order to prove the law prevailing at Rome on the subject of marriage, a Roman Catholic bishop was tendered as a witness, and was subjected to examination as to the nature and extent of the duties of his office in its bearing on the subject of marriage, with the view of ascertaining whether he had such a peculiar knowledge of the law relative to marriage as would render him competent to give evidence respecting it. It appeared from this examination, that the witness had resided more than twenty years at Rome, and had studied the ecclesiastical law prevailing there on the above subject; that a knowledge of [*725] this law *was necessary in order to the due discharge of an important part of the duties of his office; that the decision of matrimonial cases, so far as they might be affected by the ecclesiastical and canon law, fell within the jurisdiction of the Roman Catholic bishops; and, further, that the tribunals at Rome would respect and act upon his decision or judgment in any particular case if it was unappealed from. It was held, that the witness came within the definition of peritus, and was admissible accordingly.1

1 The Sussex Peerage, 11, Cl. & Fin. 85. The maxim above briefly considered is also often applicable when a question arises as to the degree of weight due to the decision of a court of distinct and independent jurisdiction. See Bunting v. Lepingwell, 4 Rep. 29; cited, Argument, Griffin v. Ellis, 11 Ad. & E. 749; E. C. L. R. 39; Burder v. Veley, 12 Ad. & E. 253; E. C. L. R. 40. See also the remarks of Lord Langdale, M. R., in Earl Nelson v. Lord Bridport, 8 Beav. 527; Baron de Bode v. Reg., 10 Jur. 217. "A long course of practice sanctioned by professional men, is often the best expositor of the law." Per Lord Eldon, C., Candler v. Candler, 1 Jac. 232.